Browsing by Author "Wilkes, Chris"

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    Modelling the spatial distribution of three marine fish species in the southern Benguela
    (2013) Wilkes, Chris; Shin, Yunne-jai; Yemane, Dawit
    Understanding the spatial distribution of species in relationship to climatic and environmental variables is key to conservation and management of important species, as their distribution might change under climate change and variability. Based on presence absence data from scientific trawl surveys, this study used Generalized Additive Model (GAM) and Krigging with External Drift (KED) statistical techniques to determine the spatial distribution of three marine fish species of commercial interest: Merluccius capensis, Merluccius paradoxus, and Thyrsites atun, on the West and South coasts of South Africa. The modelled distributions reflect the previously determined range and habitats of the two species of hake and are in accordance with the common knowledge on the biology of the two species. Presence-absence modelling found depth to be the main factor for explaining hake distribution on both coasts. For the West coast an interaction between sea surface temperature and chlorophyll-a combined with depth as a factor was found to provide the best model. On the South coast depth was the only factor retained. The models for M. capensis and M. paradoxus are potentially useful in mapping and determining future distributions based on environmental factors. The model obtained for the spatial distribution of T. atun has a lower explanatory power than those of the two hake species.
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    A study on the behaviour and reproduction of the weedsucker, Eckloniaichthys scylliorhiniceps (Smith, 1943)
    (2013) Wilkes, Chris; Attwood, Colin
    Eckloniaichthys scylliorhiniceps (Gobisociadae) is a highly abundant but little studied fish endemic to Southern Africa. Like other species in the family it adheres to substrates using its modified pelvic fins that form a disc. Observational data and samples were obtained near Simon’s Town, South Africa. The average length was found to be greater than first reported by Smith (1943) and is now 49mm for females (n=14) and 38 mm for males (n=17). The diet of the weedsucker was found to consist wholly of crustacean meiofauna. Internal fertilization occurs and females lay between 120 and 150 eggs on the fronds of kelp. Reproduction is thought to take place year round. Further work needs to be conducted on predators of weedsuckers, tentatively suggested here to be diving birds (such as Phalacrocorax capensis) and mid-level benthic predators (such as Poroderma africanum). Eckloniaichthys scylliorhiniceps is an important part of the subtidal kelp forest ecosystem as it provides a link in the trophic food web between crustacean meiofauna and higher-level predators.